This invention relates to methods and apparatus for canning food products. More particularly, it relates to methods and apparatus which are suitable for use in home canning operations. Even more particularly, the invention relates to such methods and apparatus which are suitable for use with a home microwave oven.
Home canning of various types of produce, such as fruits and vegetables, has become a popular activity in the United States. While there are many attractive reasons for such home canning, a major disadvantage to the procedure has always been the necessity for pressure cooking the food product within the container. This process has generally involved preparing the food products and placing them in containers, such as glass jars with loosely closed tops, and then placing the container and product within a pressure cooking vessel, or retort, and then applying steam to the containers and their contents for an extended period of time within the pressure cooker, to cook and sterilize the food.
The conventional apparatus and methods for home canning have suffered from a number of disadvantages which have discouraged many people from engaging in the home canning process. The disadvantages have included the necessity for expensive and bulky pressure cooking apparatus and the requirement of substantial time and heating energy to perform the pressure cooking procedure. These requirements have made home canning economically practical only when conducted on a substantial scale. Furthermore, pressure cooking of certain fruits and vegetables in the canning process destroys many desirable characteristics of the food, including crisp textures and retention of vitamins within the fruits and vegetables themselves.
A far simpler approach to this home canning process is disclosed in the co-pending patent application Ser. No. 107,425 filed Dec. 26, 1979 in the names of Max P. Beauvais and Raymond E. Camezon, now U.S. Pat. No. 4,294,167, the inventors of this application. Such application discloses a simpler apparatus for use in stove top canning operations.
In recent years the home microwave oven has enjoyed an enormous growth in popularity, largely because of the speed with which it cooks, generally taking about one fourth the time of conventional oven cooking. Although the microwave oven has provided for rapid cooking, it has not been suitable for use in conventional home canning operations for several reasons. One reason is the enormous absorption of microwave energy by any metallic objects placed within the oven cavity, such that those metallic objects would absorb a great proportion of the microwave energy, thus reducing that available for sterilizing and preparing the food. For this reason, it is generally considered highly inadvisable to place any metallic objects within a microwave oven when it is operating. Conventional home canning apparatus is almost entirely of metallic construction, even including the lids used to seal glass jars. Accordingly, none of this apparatus is suitable for use in microwave ovens. Further, even if the conventional apparatus were fabricated of a material suitable for use in a microwave oven, the relatively small (generally one cubic foot) volume of most microwave ovens precludes the use of the bulky conventional apparatus. Accordingly, until now there has been no satisfactory apparatus for convenient home canning, which can take advantage of the rapid heating of a microwave oven.